Pasteurising Straw

Pasteurising a substrate has several advantages over sterilisation. It’s more economical in terms of energy expenditure; it’s less time consuming; and you have no need for expensive cropping containers such as the use of myco/autoclavable bags. However, pasteurisation is only suitable for certain fast growing resilient species such as oyster mushrooms.


  • Straw
  • gypsum (3% dry weight of straw)


  • large pot
  • probe cooking thermometer
  • plate
  • brick
  • strainer or sieve
  • plastic bags or other suitable fruiting containers


  • cut straw into small pieces 1 – 3 inches
  • soak in soapy water for 24hrs
  • drain
  • add to water at 80c
  • stir in gypsum
  • Keep at 74c – 80c for at least 1hr
  • drain and cool
  • layer in bag or suitable fruiting container with spawn



Pre soaking the straw for 12 – 24 hours helps to hydrate the substarte if using sawdust you should consider lengthening this time to a few days changing the water once or twice during this period. Adding some washing up liquid helps remove grease and dust when you drain the substrate.

Once drained from the pre-soak add the gypsum. Now add your hot water at a temperature of 80c. Once added the temperature of the water will drop so heat the pan until the temperature reaches somewhere between 74 and 80c. Now you can simmer the pan or if you want to save energy place the pan into a hay box or wrap it up in old duvets. Leave it for an hour or two then drain and allow to cool before inoculating.

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